Phospholipids are a diverse class of amphipathic molecules present in all biological membranes. Because of the difficulties (only currently being resolved) encountered in working with membrane components, little is known about the enzymatic and genetic control of phospholipid metabolism, or about the role of individual phospholipid species in membrane function. A greater understanding of this aspect of membrane biochemistry would be desirable, since phospholipids are particularly abundant in structures susceptible to pathological processes, such as circulating lipoproteins and lung surfactant. Towards this end, the PI has been isolating and characterizing mutants defective in specific enzymes of phospholipid biosynthesis, using a versatile, rapid autoradiographic screening procedure (Raetz, C. R. H. 1975, Proc. Natl. Acad. Sci. U.S.A. 72, 2274-2278). Mutants under investiation include strains defective in phosphatidylserine and phosphatidylglycerophosphate synthetases, diglyceride kinase, and CDP-diglyceride synthetase. With these organisms, which were not available until recently, it is possible to vary the phospholipid composition, particularly the "polar headgroups," and to introduce unusual phospholipids, which are not ordinarily present, into the cell membrane. In the coming grant period the growth properties, composition, and membrane function of these mutants will be examined and compared to wild type strains. All of the studies described in this proposal will be carried out with the simple bacterium, Escherichia coli, but the approach used here is equally applicable to eucaryotic systems.